A Mobile DNP Polarizer for Continuous Flow Applications

Abstract

Despite its wide applicability in natural sciences, nuclear magnetic resonance (NMR) still suffers from its inherently low sensitivity. This could be overcome by hyperpolarization of molecules via dynamic nuclear polarization (DNP). Here, we introduce a substantial improvement of a mobile Overhauser DNP polarizer, based on an inexpensive Halbach magnet operating at 0.35 T. It shows an almost vanishing magnetic flux at its outer side and does not disturb other instruments. It can be placed directly next to a superconducting magnet, thus reducing the transport time of the hyperpolarized liquid. However, two problems for DNP applications remain. Firstly, radicals are needed which are often toxic. This problem becomes crucial with regard to medical applications. Secondly, the sample must be transported from the polarization magnet to the place of detection like a magnetic resonance imaging (MRI) scanner, and polarization losses due to T 1 relaxation may occur. We have implemented a flow system into the mobile DNP polarizer, which overcomes both obstacles. The radicals are immobilized in a gel matrix and the hyperpolarized radical-free fluid is subsequently directly pumped into the MRI scanner. It is shown that even at flow conditions, the NMR signal is enhanced due to Overhauser DNP in the Halbach magnet as well as in the MRI scanner (4.7 T) at a distance of 1.4 m. Acquired images demonstrate the use of enhanced and, due to dipolar coupling, inverted NMR signals, which provide an excellent MRI contrast even for small enhancements.

Optimization and prediction of the electron–nuclear dipolar and scalar interaction in1H and13C liquid state dynamic nuclear polarization

“…53 , 54 The use of immobilized radicals for DNP approaches has recently been reconsidered and utilized to generate hyperpolarized water for clinical MRI applications. 11 – 13 , 55 , 56 The efficiency of interactions between the radical and nuclei in immobilized radical flow methods can be in fact improved through better design of immobilizing methods, 11 , 57 as well as the optimum synthesis of new radicals. 58 – 60 …”

Overhauser dynamic nuclear polarization (ODNP)-enhanced two-dimensional proton NMR spectroscopy at low magnetic fields

“…As a new application, high-resolution ODNP-enhanced JRES spectroscopy enables site-specific, chemical shiftresolved solvent dynamics measurements. For example, ODNP measurements on toluene show different saturation behavior for the methyl and aromatic protons in toluene, suggesting different solvent dynamics for the different proton sites (Enkin et al, 2014;Keller et al, 2020). Since the peak separation is only about 4 ppm, highly homogenous magnetic fields are required to study the peaks individually since overlapping peaks will make data analysis more difficult.…”

Optical hyperpolarization of heteronuclear spin singlet order in liquids

“…When the radius of the ND is 5 nm, suppose the flow channel is composed of a tube of a diameter of 1 mm, the size of the hydrogel layer is 1 mm and the resulting volume is filled with NDs of 10nm diameter such that they account for 12% of the total volume. We choose the flow rate of v = 10 −3 m/s (this flow rate is achieved with commercial pumps, where flow rates over 10 times larger have been achieved in similar systems [26], and negligibly affects the molecular dynamics within τ c ) such that t 1 ∼ 1s. Formic acid samples are used with mixtures of 13 C-labeled formic acid and H 2 O (in the proportion 10:1).…”